Riding lawn mowers are well known and typically comprise wheeled frames having an engine, a seat for supporting an operator, and a cutting deck having a rotary blade for cutting grass or other ground growing vegetation. A transmission suitably connects the engine to the rear or driving wheels of the lawn mower for self-propelling the mower over the ground. In many cases, such lawn mowers also include a pair of steerable front wheels controlled by a steering wheel adjacent the operator's seat. The operator sits on the seat and controls the operation of the mower, i.e. its direction, its speed of movement, the operation of the cutting deck, etc., by suitable manipulation of various control elements, i.e. the steering wheel, a throttle control and/or a gear selection lever on the transmission, a blade engagement lever, etc.
In using riding lawn mowers, there are often many situations in which a mower having a high degree of maneuverability is desirable. For example, if the area to be mowed has a number of trees or bushes, or if there are tight spots into which the mower must go, then maneuverability is quite important to the speedy conclusion of the job. Most conventional riding mowers of the type described above, in which the rear wheels are continuously driven, are not as maneuverable as one would like due to their relatively large turning radius.
Accordingly, various mowers having a small or zero turning radius have attempted to increase rider maneuverability. Many such mowers use less stable front caster wheel or three wheel arrangements rather than a true four wheel configuration. Many such mowers do not have a conventional steering wheel, but use two control levers or joysticks which the operator has to manipulate to clutch and declutch the rear driven wheel on the inside of the turn. Such controls are confusing for most people to use and this decreases the safety of operation.
In addition, many prior art ZTR mowers use a differential to drive the rear wheels. When such mowers are turned sharply in a ZTR fashion, i.e. by decreasing the drive to one of the drive wheels, they speed up in an undesirable fashion. This speed increase can be startling to the operator and increases the forces on the operator tending to throw the operator off the machine. This again makes safe operation of the product somewhat more difficult. Moreover, many known ZTR's also effect a sharp turn by completely braking or stopping the drive wheel on the inside of the turn. In many cases, this tears a divot in the turf at the spot of the braked wheel, which is obviously undesirable.